1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a low noise amplifier (LNA), and more particularly, to a full differential LNA having a differential input and differential output structure and a method of using the same, capable of reducing noise figure, a design area, and power consumption.
2. Description of the Related Art
Currently, wireless devices such as a radio frequency ID (RFID) reader, a mobile phone, and a personal digital assistant (PDA) generally employ a direct conversion method instead of a super-heterodyne method, as an RF signal receiving method. Since an intermediate frequency is not used in the direct conversion method, components for a corresponding processing may be saved, thereby reducing cost, decreasing weight, and enabling a system on a chip. However, performance of a mixer used for directly converting a signal of a baseband into a carrier wave or converting a received RF signal into a signal of a baseband, in wireless devices, is deteriorated due to some signal distortion caused by second order intercept point (IP2). A low noise amplifier (LNA) amplifying a signal in front of the mixer has to be designed for reducing the above noise component IP2 as well as design area and power consumption.
FIG. 1 illustrates an example of a related art cascode amplifier 100. Referring to FIG. 1, the cascode amplifier 100 includes transistors M11, M12, M13, and M14 and inductors L11, L12, L13, and L14. The cascode amplifier 100 is a related art differential LNA in the structure of combining a common source and a common gate. In FIG. 1, an input impedance of input differential signal terminals IN_P and IN_N, output impedances of terminals of output differential signals OUT_P and OUT_N, and a gain are determined depending on load inductors L11 and L12, degeneration inductors L13 and L14, and bias voltage VB.
However, while it is known as the cascode amplifier 100 reuses current and has certain stability, it is difficult to acquire a low-Q since the input impedance and the output impedance are high, and therefore impedance matching is not simple, and it is difficult to expand an operational bandwidth.
FIG. 2 illustrates an example of a related art push-pull amplifier 200. Referring to FIG. 2, the push-pull amplifier 200 includes transistors M21 and M22 and inductors L21 and L22. In the push-pull amplifier 200, an N-channel metal-oxide-semiconductor field effect transistor (MOSFET) M21 and a P-channel MOSFET M22 perform complementary operations and an input impedance of an input signal (LNA_IN) terminal, an output impedance of an output signal LNA_OUT terminal, and a gain are determined depending on transconductance of the transistors M21 and M22.
However, while the push-pull amplifier 200 has certain high power efficiency and the low input impedance, the output impedance is high. Accordingly, in the push-pull amplifier 200, an impedance matching as well as a low-Q is not easy at the output terminal, and it is difficult to expand an operational bandwidth.